The evolving landscape of protein kinases in breast cancer: clinical implications

Considerations for the design of antibody drug conjugates (ADCs) for clinical development: lessons learned

Antibody-drug conjugates (ADCs) have emerged as a novel therapeutic strategy that has successfully reached patient treatment in different clinical scenarios. ADCs are formed by an antibody against a specific tumor-associated antigen (TAA), a cytotoxic payload, and a chemical linker that binds both. To this regard, most efforts have been focused on target identification, antibody design and linker optimization, but other relevant aspects for clinical development have not received the necessary attention. In this article using data from approved ADCs, we evaluated all characteristics of these agents, including payload physicochemical properties, in vitro potency, drug antibody ratio (DAR), exposure-response relationships, and clinical development strategies. We suggest that compounds with best options for clinical development include those with optimal payload physicochemical properties and cleavable linkers that would lead to a bystander effect. These modalities can facilitate the development of ADCs in indications with low expression of the TAA. Early clinical development strategies including changes in the schedule of administration with more frequent doses are also discussed in the context of an efficient strategy. In conclusion, we highlight relevant aspects that are needed for the optimal development of ADCs in cancer, proposing options for improvement.

Endocrine therapy resistance: what we know and future directions

Endocrine resistance is a major hurdle in the treatment of estrogen receptor (ER)-positive breast cancer. When abnormally regulated, molecular signals responsible for cellular proliferation, as well as ER itself, allow for cellular evasion of ER-dependent treatments. Therefore, pharmacological treatments that target these evasion mechanisms are beneficial for the treatment of endocrine-resistant breast cancers. This review summarizes currently understood molecular signals that contribute to endocrine resistance and their crosstalk that stem from mitogen-activated protein kinase (MAPK), phosphoinositol-3 kinase/protein kinase B (PI3K/AKT), mechanistic target of rapamycin (mTOR), cyclin-dependent kinases 4 and 6 (CDK4/6) and aberrant ER function. Recent clinical trials that target these molecular signals as a treatment strategy for endocrine-resistant breast cancer are also highlighted.

Arbutin suppresses osteosarcoma progression via miR-338-3p/MTHFD1L and inactivation of the AKT/mTOR pathway

Arbutin, a glycoside extracted from the plant Arctostaphylos uva‐ursi, has been previously reported to possess antioxidant, anti‐inflammatory and anticancer effects. Here, we investigated whether arbutin affects the proliferation of the cells of the osteosarcoma (OS) cell lines MG‐63 and SW1353. Arbutin suppressed OS cell viability in a dose‐ and time‐dependent manner, as shown by Cell Counting Kit‐8 assay. Furthermore, arbutin exposure decreased the protein levels of MTHFD1L, CCND1 and phosphorylated‐protein kinase B (AKT)/phosphorylated‐mammalian target of rapamycin (mTOR). Potential upstream miRNAs of MTHFD1L were predicted using TargetScan, PICTAR5, miRanda and miRWalk. We performed luciferase activity assays to show that miR‐338‐3p directly targets and negatively regulates the expression of MTHFD1L. Knockdown of miR‐338‐3p promoted cell invasion, migration and proliferation in arbutin‐treated OS cells via MTHFD1L. In summary, our data suggest that arbutin inhibits OS cell proliferation, migration and invasion via miR‐338‐3p/MTHFD1L and by inactivating the AKT/mTOR pathway.

CD26 upregulates proliferation and invasion in keloid fibroblasts through an IGF-1-induced PI3K/AKT/mTOR pathway

Background

Keloid is a fibrotic dermal disease characterized by an abnormal increase in fibroblast proliferation and invasion. These pathological behaviours may be related to the heterogeneity of keloid fibroblasts (KFs); however, because of a lack of effective biomarkers for KFs it is difficult to study the underlying mechanism. Our previous studies revealed that the expansion of CD26⁺ KFs was responsible for increased keloid proliferation and invasion capabilities; the intrinsic relationship and mechanism between CD26 and keloid is therefore worthy of further investigation. The aim of this study was to explore molecular mechanisms in the process of CD26 upregulated KFs proliferation and invasion abilities, and provide more evidence for CD26 as an effective biomarker of keloid and a new clinical therapeutic target.

Methods

Flow cytometry was performed to isolate CD26⁺/CD26⁻ fibroblasts from KFs and normal fibroblasts. To generate stably silenced KFs for CD26 and insulin-like growth factor-1 receptor (IGF-1R), lentiviral particles encoding shRNA targeting CD26 and IGF-1R were used for transfection. Cell proliferations were analysed by cell counting kit-8 assay and 5-ethynyl-2′-deoxyuridine (EdU) incorporation assay. Scratching assay and transwell assay were used to assess cell migration and invasion abilities. To further quantify the regulatory role of CD26 expression in the relevant signalling pathway, RT-qPCR, western blot, ELISA, PI3K activity assay and immunofluorescence were used.

Results

Aberrant expression of CD26 in KFs was proven to be associated with increased proliferation and invasion of KFs. Furthermore, the role of the IGF-1/IGF-1 receptor axis was also studied in CD26 and was found to upregulate KF proliferation and invasion. The PI3K/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway was shown to affect CD26-regulated KF proliferation and invasion by increasing phosphorylation levels of S6 kinase and 4E-binding protein.

Conclusions

CD26 can be the effective biomarker for KFs, and its expression is closely related to proliferation and invasion in keloids through the IGF-1-induced PI3K/AKT/mTOR pathway. This work provides a novel perspective on the pathological mechanisms affecting KFs and therapeutic strategies against keloids.

Short hairpin RNA-mediated gene silencing of ADAM17 inhibits the growth of breast cancer MCF‑7 cells in vitro and in vivo and its mechanism of action

A disintegrin and metalloprotease 17 (ADAM17) is highly expressed in many malignant tumors and is closely related to their development. We showed in a previous study that silencing of ADAM17 by siRNA inhibited the growth of MCF-7 breast cancer cells in vitro and in vivo. In the present study, we investigated the effects of ADAM17-short hairpin RNA (ADAM17-shRNA) on MCF-7 breast cancer cells and explored the potential action pathway. In vitro, transfection of shRNAs was performed using a lentivirus, and the effects of ADAM17-shRNA on invasion, proliferation and cell cycle distribution of MCF-7 cells were assessed by Boyden chamber method, real-time cell analysis and flow cytometry, respectively. In vivo, MCF-7 cells with different administrations were transplanted subcutaneously into nude mice, and the effect of ADAM17-shRNA on the growth of transplanted tumors was assessed. In addition, the morphological structures were observed by H&E staining, and the expression of ADAM17 and Ki-67 was assessed by immunohistochemistry; expression of ADAM17, EGFR, p-EGFR, AKT, p-AKT, ERK and p-ERK proteins was assessed by western blotting, respectively. Our data showed that ADAM17-shRNA successfully inhibited ADAM17 mRNA expression, invasion and proliferation of MCF-7 cells resulting in G0/G1 phase arrest, and significantly inhibited the growth of transplanted tumors with larger areas of necrosis, low expression of ADAM17 and Ki-67 and reduced protein expression of ADAM17, EGFR, p-EGFR, AKT, p-AKT, ERK, and p-ERK in the tumor tissues. The present research suggests that ADAM17-shRNA can inhibit MCF-7 cell invasion and proliferation in vitro and inhibit MCF-7 xenograft growth in vivo through the EGFR/PI3K/AKT and EGFR/MEK/ERK signaling pathways.

Novel application of the published kinase inhibitor set to identify therapeutic targets and pathways in triple negative breast cancer subtypes

Triple negative breast cancers (TNBCs) have high recurrence and metastasis rates. Acquisition of a mesenchymal morphology and phenotype in addition to driving migration is a consequential process that promotes metastasis. Although some kinases are known to regulate a mesenchymal phenotype, the role for a substantial portion of the human kinome remains uncharacterized. Here we evaluated the Published Kinase Inhibitor Set (PKIS) and screened a panel of TNBC cell lines to evaluate the compounds’ effects on a mesenchymal phenotype. Our screen identified 36 hits representative of twelve kinase inhibitor chemotypes based on reversal of the mesenchymal cell morphology, which was then prioritized to twelve compounds based on gene expression and migratory behavior analyses. We selected the most active compound and confirmed mesenchymal reversal on transcript and protein levels with qRT-PCR and Western Blot. Finally, we utilized a kinase array to identify candidate kinases responsible for the EMT reversal. This investigation shows the novel application to identify previously unrecognized kinase pathways and targets in acquisition of a mesenchymal TNBC phenotype that warrant further investigation. Future studies will examine specific roles of the kinases in mechanisms responsible for acquisition of the mesenchymal and/or migratory phenotype.

Efficacy of neratinib in the treatment of HER2/neu-amplified epithelial ovarian carcinoma in vitro and in vivo

Epithelial ovarian carcinoma is the most lethal of gynecologic malignancies. There is a need to optimize the currently available treatment strategies and to urgently develop novel therapeutic agents against chemotherapy-resistant disease. The objective of our study was to evaluate neratinib's preclinical efficacy in treating HER2-amplified ovarian cancer. Neratinib's efficacy in treating HER2-amplified ovarian cancer was studied in vitro utilizing six primary tumor cell lines with differential HER2/neu expression. Flow cytometry was utilized to assess IC₅₀, cell signaling changes, and cell cycle distribution. Neratinib's in vivo efficacy was evaluated in HER2-amplified epithelial ovarian carcinoma xenografts. Three of six (50%) ovarian cancer cell lines were HER2/neu-amplified. Neratinib showed significantly higher efficacy in treating HER2/neu-amplified cell lines when compared to the non-HER2/neu-amplified tumor cell lines (mean ± SEM IC₅₀:0.010 μM ± 0.0003 vs. 0.076 μM ± 0.005 p < 0.0001). Neratinib treatment significantly decreased the phosphorylation of the transcription factor S6, leading to arrest of the cell cycle in G0/G1 phase. Neratinib prolonged survival in mice harboring HER2-amplified epithelial ovarian carcinoma xenografts (p = 0.003). Neratinib inhibits proliferation, signaling, cell cycle progression and tumor growth of HER2-amplified epithelial ovarian carcinoma in vitro. Neratinib inhibits xenograft growth and improves overall survival in HER2/neu-amplified ovarian cancer in vivo. Clinical trials are warranted.

Phospho-kinase profile of colorectal tumors guides in the selection of multi-kinase inhibitors

Protein kinases play a central role in the oncogenesis of colorectal tumors and are attractive druggable targets. Detection of activated kinases within a tumor could open avenues for drug selection and optimization of new kinase inhibitors. By using a phosphokinase arrays with human colorectal tumors we identified activated kinases, including the Epidermal Growth Factor Receptor (EGFR), components of the PI3K/mTOR pathway (AKT and S6), and STAT, among others. A pharmacological screening with kinase inhibitors against these proteins helped us to identify a new kinase inhibitor, termed EC-70124 that showed the highest anti-proliferative activity in cell lines. EC-70124 also inhibited cell migration and biochemical experiments demonstrated its effect targeting the PI3K/mTOR pathway. This drug also arrested cells at G2/M and induced apoptosis. Experiments in combination with standard chemotherapy used in the clinical setting indicated a synergistic effect. EC-70124 also reduced tumor growth in vivo and inhibited pS6 in the implanted tumors. In conclusion, by studying the kinase profile of colorectal tumors, we identified relevant activated pathways, and a new multi-kinase compound with significant antitumor properties.

Identification of therapeutic targets in ovarian cancer through active tyrosine kinase profiling

The activation status of a set of pro-oncogenic tyrosine kinases in ovarian cancer patient samples was analyzed to define potential therapeutic targets. Frequent activation of HER family receptor tyrosine kinases, especially HER2, was observed. Studies in ovarian cancer cell lines confirmed the activation of HER2. Moreover, knockdown of HER2 caused a strong inhibition of their proliferation. Analyses of the action of agents that target HER2 indicated that the antibody drug conjugate trastuzumab-emtansine (T-DM1) caused a substantial antitumoral effect in vivo and in vitro, and potentiated the action of drugs used in the therapy of ovarian cancer. T-DM1 provoked cell cycle arrest in mitosis, and caused the appearance of aberrant mitotic spindles in cells treated with the drug. Biochemical experiments confirmed accumulation of the mitotic markers phospho-Histone H3 and phospho-BUBR1 in cells treated with the drug. Prolonged treatment of ovarian cancer cells with T-DM1 provoked the appearance of multinucleated cells which later led to cell death. Together, these data indicate that HER2 represents an important oncogene in ovarian cancer, and suggest that targeting this tyrosine kinase with T-DM1 may be therapeutically effective, especially in ovarian tumors with high content of HER2.

P53- and mevalonate pathway-driven malignancies require Arf6 for metastasis and drug resistance

Drug resistance, metastasis, and a mesenchymal transcriptional program are central features of aggressive breast tumors. The GTPase Arf6, often overexpressed in tumors, is critical to promote epithelial-mesenchymal transition and invasiveness. The metabolic mevalonate pathway (MVP) is associated with tumor invasiveness and known to prenylate proteins, but which prenylated proteins are critical for MVP-driven cancers is unknown. We show here that MVP requires the Arf6-dependent mesenchymal program. The MVP enzyme geranylgeranyl transferase II (GGT-II) and its substrate Rab11b are critical for Arf6 trafficking to the plasma membrane, where it is activated by receptor tyrosine kinases. Consistently, mutant p53, which is known to support tumorigenesis via MVP, promotes Arf6 activation via GGT-II and Rab11b. Inhibition of MVP and GGT-II blocked invasion and metastasis and reduced cancer cell resistance against chemotherapy agents, but only in cells overexpressing Arf6 and components of the mesenchymal program. Overexpression of Arf6 and mesenchymal proteins as well as enhanced MVP activity correlated with poor patient survival. These results provide insights into the molecular basis of MVP-driven malignancy.

Transcriptomic analyses identify association between mitotic kinases, PDZ-binding kinase and BUB1, and clinical outcome in breast cancer

Protein kinases are important components in oncogenic transformation of breast cancer. Evaluation of upregulated genes that codify for protein kinases could be used as biomarkers to predict clinical outcome. Gene expression and functional analyses using public datasets were performed to identify differential gene expression and functions in basal-like tumors compared with normal breast tissue. Overall survival (OS) associated with upregulated genes was explored using the KM Plotter online tool. The prognostic influence of these genes in luminal tumors and systemically untreated patients was also assessed. Of the 426 transcripts identified in basal-like tumors, 11 genes that coded for components of protein kinases were upregulated with more than a fourfold change. Regulation of cell cycle was an enriched function containing 10 of these 11 identified genes. Among them, expression of four genes, BUB1β, CDC28, NIMA, and PDZ binding kinase, were all associated with improved OS when using at least one probe in the basal-like subtype. Two genes, BUB1β and PDZ binding kinase, showed consistent association with improved OS irrespective of the gene probe used for the analysis. No association was observed for these genes with relapse-free survival. In contrast, both BUB1β and PDZ binding kinase showed worse OS in luminal tumors and in a cohort of systemically untreated patients. BUB1β and PDZ binding kinase are associated with improved OS in basal-like tumors and worse OS in luminal and untreated patients. The association with a better outcome in basal-like tumors could be due to a more favorable response to chemotherapy.

mTOR pathway protein immunoexpression as a prognostic factor for survival in head and neck cancer patients: a systematic review and meta-analysis

BACKGROUND

Several mTOR pathway proteins are involved in the regulation of cellular anabolism, growth, proliferation, and survival. Activated proteins in the mTOR pathway are deregulated in multiple types of cancers and could influence prognosis. However, it is unclear whether deregulation of mTOR pathway proteins serves a prognostic role in patients with head and neck cancer (HNC). Furthermore, proteins in the mTOR pathway may be important targets for anticancer therapy. The aim of this study was to summarize existing cohort studies to determine whether immunoexpression of mTOR pathway proteins are important prognostic factors for survival in patients with HNC.

MATERIALS AND METHODS

A systematic review was performed using the Cochrane, Lilacs, PubMed, ScienceDirect, Scopus, and Web of Science databases (up to 23 January 2015). A meta-analysis was conducted to measure the frequency of protein expression in head and neck cancer patient samples and the prognostic value of mTOR pathway proteins for overall survival (OS) and disease-free survival (DFS).

RESULTS

Twelve studies were included in our final analysis. The meta-analysis revealed that the frequency of overall expression of mTOR pathway proteins was 74.42% (CI: 63.3 to 84.0, P < 0.001, n = 2016 samples). The survival meta-analysis showed a pooled hazard ratio for OS and DFS of 1.44 (95% confidence interval [95% CI] 1.14-1.73) and 1.18 (95% CI 0.71-1.64), respectively.

CONCLUSION

This systematic review and meta-analysis support evidence that mTOR pathway proteins can be used as predictive markers for survival in patients with HNC because their expression was significantly associated with poor OS and short DFS.

Biological insights into effective and antagonistic combinations of targeted agents with chemotherapy in solid tumors

The potential for synergistic interactions between anticancer drugs has been used to justify combinations of agents in clinical trials. However, most combinations of targeted agents and chemotherapies have been tested in the clinic without previous systematic evaluation of their potential benefit. Preclinical studies may help in the identification of synergistic or antagonistic interactions. For antineoplastic therapies, these studies may reveal synergy or antagonism of the drug combinations. Synergy occurs when two agents given together produce higher antitumoral activity than the sum of each individual drug. This represents the ideal setting for the development of combinations of targeted agents and chemotherapies. On the other side, certain drug combinations have shown adverse results, indicative of an antagonistic effect. In this article, we review the preclinical molecular bases that justify approved combinations of targeted agents with chemotherapy including examples of synergistic and antagonistic combinations. We also discuss scenarios for rational associations of targeted agents based on biological data and propose strategies that may improve the success of combinations of anticancer agents.

Targeting ADAM-17 with an inhibitory monoclonal antibody has antitumour effects in triple-negative breast cancer cells

Background:

Identification and validation of a targeted therapy for triple-negative breast cancer (TNBC), that is, breast cancers negative for oestrogen receptors, progesterone receptors and HER2 amplification, is currently one of the most urgent problems in breast cancer treatment. EGFR is one of the best-validated driver genes for TNBC. EGFR is normally activated following the release of ligands such as TGFα, mediated by the two MMP-like proteases ADAM (a disintegrin and metalloproteinase)-10 and ADAM-17. The aim of this study was to investigate the antitumour effects of a monoclonal antibody against ADAM-17 on an in vitro model of TNBC.

Methods:

We investigated an inhibitory cross-domain humanised monoclonal antibody targeting both the catalytic domain and the cysteine-rich domain of ADAM17-D1(A12) in the HCC1937 and HCC1143 cell lines.

Results:

D1(A12) was found to significantly inhibit the release of TGFα, and to decrease downstream EGFR-dependent cell signalling. D1(A12) treatment reduced proliferation in two-dimensional clonogenic assays, as well as growth in three-dimensional culture. Furthermore, D1(A12) reduced invasion of HCC1937 cells and decreased migration of HCC1143 cells. Finally, D1(A12) enhanced cell death in HCC1143 cells.

Conclusion:

Our in vitro findings suggest that targeting ADAM-17 with D1(A12) may have anticancer activity in TNBC cells.

Translation in solid cancer: are size-based response criteria an anachronism?

The purpose of translation is the development of effective medicinal products based on validated science. A parallel objective is to obtain marketing authorization for the translated product. Unfortunately, in solid cancer, these two objectives are not mutually consistent as evidenced by the contrast between major advances in science and the continuing dismal record of pharmaceutical productivity. If the problem is unrelated to science, then the process of translation may require a closer examination, namely, the criteria for regulatory approval. This realization is important because, in this context, the objective of translation is regulatory approval, and science does not passively translate into useful medicinal products. Today, in solid cancer, response criteria related to tumor size are less useful than during the earlier cytotoxic drugs era; advanced imaging and biomarkers now allow for tracking of the natural history of the disease in the laboratory and the clinic. Also, it is difficult to infer clinical benefit from tumor shrinkage since it is rarely sustained. Accordingly, size-based response criteria may represent an anachronism relative to translation in solid cancer and it may be appropriate to align preclinical and clinical effort and shift the focus to local invasion and metastasis. The shift from a cancer cell-centric model to a stroma centric model offers novel opportunities not only to interupt the natural history of the disease, but also to rethink the relevance of outdated criteria of clinical response. Current evidence favors the opinion that, in solid cancer, a different, broader, and contextual approach may lead to interventions that could delay local invasion and metastasis. All elements supporting this shift, especially advanced imaging, are in place.

Activation of the PI3K/mTOR/AKT pathway and survival in solid tumors: systematic review and meta-analysis

BACKGROUND

Aberrations in the phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR)/AKT pathway are common in solid tumors. Numerous drugs have been developed to target different components of this pathway. However the prognostic value of these aberrations is unclear.

METHODS

PubMed was searched for studies evaluating the association between activation of the PI3K/mTOR/AKT pathway (defined as PI3K mutation [PIK3CA], lack of phosphatase and tensin homolog [PTEN] expression by immunohistochemistry or western-blot or increased expression/activation of downstream components of the pathway by immunohistochemistry) with overall survival (OS) in solid tumors. Published data were extracted and computed into odds ratios (OR) for death at 5 years. Data were pooled using the Mantel-Haenszel random-effect model.

RESULTS

Analysis included 17 studies. Activation of the PI3K/mTOR/AKT pathway was associated with significantly worse 5-year survival (OR:2.12, 95% confidence intervals 1.42-3.16, p<0.001). Loss of PTEN expression and increased expression/activation of downstream components were associated with worse survival. No association between PIK3CA mutations and survival was observed. Differences between methods for assessing activation of the PI3K/mTOR/AKT pathway were statistically significant (p = 0.04). There was no difference in the effect of up-regulation of the pathway on survival between different cancer sites (p = 0.13).

CONCLUSION

Activation of the PI3K/AKT/mTOR pathway, especially if measured by loss of PTEN expression or increased expression/activation of downstream components is associated with poor survival. PIK3CA mutational status is not associated with adverse outcome, challenging its value as a biomarker of patient outcome or as a stratification factor for patients treated with agents acting on the PI3K/AKT/mTOR pathway.

Phosphorylation of P-Rex1 at serine 1169 participates in IGF-1R signaling in breast cancer cells

Former reports demonstrated that P-Rex, a Rac guanine nucleotide exchange factor (GEF), participated in signaling upon activation of the ErbB receptor tyrosine kinases (RTKs). Activation of ErbB receptors turned on a phosphorylation/dephosphorylation cycle of P-Rex in which stimulation of serine(1169) phosphorylation played a critical role in the activation of this GEF. This precedent raised the important question of whether this P-Rex1 activation mechanism was restricted to ErbB receptors or could represent a general signaling event shared by several RTKs. To explore that possibility the effect of activation of distinct RTKs on the phosphorylation of P-Rex1 at serine(1169) was analyzed. Here we report that IGF-1 and FGF receptors activate serine(1169) phosphorylation of P-Rex1. P-Rex1 phosphorylation was required for IGF-1-induced up-regulation of Rac activity and cell proliferation. Moreover, IGF-1-induced adhesion was impaired in MCF7 breast cancer cells by knocking down P-Rex1. These results demonstrate that phosphorylation P-Rex1 at S(1169) represents a mechanism of activation of P-Rex1 common to multiple RTKs. We suggest that P-Rex proteins may act as novel and important transducers of pro-oncogenic signals that emanate from RTKs, and could even participate in other biological responses, such as metabolic control, which are not strictly related to the proliferation effects of RTKs.